Vinyl end-capped polyimide oligomers

ABSTRACT

The products of the invention are vinyl end-capped oligomers which are prepared from 2,4-bis (p-aminobenzyl) aniline and a vinyl substituted aromatic monoamine, the principal component of which is the compound whose structure is shown in FIG. 3. The products are prepared from either of two (2) precursors. The first precursor is a compound whose structure is shown in FIG. 2 and which is prepared from 2,4-bis (p-aminobenzyl) aniline, a dianhydride of an aromatic tetracarboxylic acid such as 3,3&#39;4,4&#39;-benzophenonetetracarboxylic acid (BTDA) and a vinyl substituted aromatic monoamine, such as 3-aminophenyl-ethylene (APE). The second precursor is a complex amine salt having the structure shown in FIG. 6 and which is prepared from 2,4-bis-(p-aminobenzyl) aniline, a dialkyl ester of BTDA and APE.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,845,018 and U.S. Pat. No. 3,879,349 disclose certainacetylene end-capped polyimide oligomers. Moldings prepared from suchresin have excellent physical properties which are largely retained attemperatures as high as 316° C. (600° F.).

The polyimides disclosed in these patents must be prepared from aromaticdiamines of specific structures to obtain the desired high temperatureperformance properties. Unfortunately such amines are difficult tosynthesize and are expensive. The synthesis also requires employment ofaminoarylacetylenes which are difficult to synthesize and are expensive.As a consequence, the polyimides of U.S. Pat. No. 3,845,018 and U.S.Pat. No. 3,879,349 can be employed only where critical operationalrequirements can justify unusually high material costs.

For the above reasons, there is a need in the art for polyimides havinggood high temperature performance properties which can be prepared frompolyamines that can be more easily synthesized and be made available atlower cost.

SUMMARY OF THE INVENTION

The products of the invention are vinyl end-capped oligomers which areprepared from an aromatic triamine such as 2,4-bis(p-aminobenzyl)aniline and a vinyl substituted aromatic monoamine, the principalcomponent of which is the compound whose structure is shown in FIG. 3.The invention also is directed to two (2) precursors of the vinylend-capped oligomers. The first precursor is a reaction product of anaromatic triamine and a vinyl substituted aromatic monoamine containingamic-acid groups, the principal component of which is the compound whosestructure is shown in FIG. 2. The second precursor is a complex aminesalt prepared in part from an aromatic triamine and a vinyl substitutedaromatic monoamine, the principal component of which is the salt shownin FIG. 6.

THE DRAWINGS

FIG. 1 is the chemical structure of an intermediate compound employed toprepare the compound of FIG. 2.

FIG. 2 is the chemical structure of a precursor of the end-cappedpolyimides of FIG. 3.

FIG. 3 is the structure of the end-capped polyimides of the invention.

FIG. 3' is the structure of a preferred species of the genericend-capped polyimides illustrated in FIG. 3.

FIG. 4 is a low polymer of the product of FIG. 3'.

FIG. 5 is the chemical structure of an intermediate compound employed toprepare the compound of FIG. 6.

FIG. 6 is the chemical structure of a second precursor of the end-cappedpolyimides of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The vinyl end-capped polyimide oligomers can be prepared by twoalternate synthesis methods subsequently designated as Synthesis MethodA and Synthesis Method B.

Synthesis Method A

In the first step of this method, substantially three (3) mols of adianhydride of an aromatic tetracarboxylic acid such as 3,3'4,4'benzophenonetetracarboxylic acid dianhydride (BTDA) are reacted with one(1) mol of an aromatic triamine in a selected class of solvents undercontrolled temperature conditions. Letting the structure of thedianhydride be represented as: ##STR1## and the structure of thetriamine be represented as ##STR2## (the structure of R and R' beingdefined infra) the principal product of this first reaction has thestructure shown in FIG. 1.

In the second step of this method, a vinyl substituted aromaticmonoamine such as 3-aminophenyl ethylene (APE) is reacted with thereaction product of the first step of the process. Letting the structureof the vinyl substituted aromatic monoamine be represented as:

    H.sub.2 N--R"

(the structure of R" being defined infra), the principal product of thesecond reaction has the structure shown in FIG. 2.

In the third step of this method, the reaction product of the secondstep is subjected to a dehydration reaction of the type known andreported in the literature to effect ring closure of the amic-acidgroups to form imide groups. The product of this step is the desiredvinyl end-capped polyimide oligomer. The principal compound of theoligomer has the structure shown in FIG. 3. FIG. 3' shows the structureof the preferred species in which aromatic triamine employed in thesynthesis in 2,4-bis (p-aminobenzyl) aniline (BPABA).

In the first step of the process, the dianhydride of the aromatictetracarboxylic acid employed will have the structure of formula 1:##STR3## where R has the structure: ##STR4## where X is ##STR5## or abond. Examples of suitable compounds conforming to formula 1 include3,3'4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA),3,3'4,4'diphenyl tetracarboxylic acid dianhydride,2,2-bis(3,4-dicarboxyphenyl) propane dianhydride,bis(3,4-dicarboxyphenyl) ether dianhydride,naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl) methane dianhydride, bis(3,4-carboxyphenyl)sulfone dianhydride, and the like. Such compounds are known and reportedin the art.

The solvent employed should be one having good solvent power for thedianhydride of formula 1 and the first intermediate product shown inFIG. 1. Suitable solvents include N-methyl-2-pyrrolidone (NMP),cyclohexanone, diethyl carbonate and gamma-butyrolactone. NMP is thesolvent of choice.

In the first step of the process, the dianhydride of formula (1) such asBTDA* is heated in one of the limited class of solvents previouslydescribed, preferably NMP, to prepare a solution containing a minimum ofat least 17 weight % of BTDA. In this step of the process, the BTDAshould be dissolved in the solvent at a temperature substantially higherthan will be employed in subsequent steps of the process. Typically theBTDA will be dissolved in the solvent at a temperature of at least 150°C. and temperatures as high as 200° C. can be employed. By operating atthese temperatures, it is possible to dissolve substantially more BTDAthan will dissolve at the reaction temperatures employed in subsequentsteps of the process. Upon cooling such solutions to the lowertemperatures subsequently employed in the reactions, it is observed thatthe BTDA does not precipitate but stays in solution, presumably byreason of the super cooling.

The quantity of BTDA dissolved in the solvent will be dictated by thesolids desired in the intermediate solution and also by the quantity ofsolvent (if any) employed to dissolve the reactants employed insubsequent steps of the process. It is possible to prepare NMP solutionscontaining up to 50 weight % BTDA which remain liquid at a temperatureof 50° C. It is preferred to prepare a solution containing a minimum of17 weight % BTDA.

In the second step of the process, the hot solution of BTDA is cooled tothe temperature which will be employed in the subsequent steps of theprocess. This temperature will be influenced by a multitude of factors.Temperatures as low as about 25° C. are sufficiently high to run thesubsequent reactions, but somewhat higher temperatures may be requiredto maintain a sufficient quantity of BTDA in solution. Solutions of BTDAare quite viscous and increasing the temperature provides easier mixingof the reactants. Temperatures above 100° C. should be avoided, as theuse of high temperatures promotes imidization of the amic acid groupspresent in the structure shown in FIG. 1. Such imidization isundesirable as the imide group containing products have reducedsolubility in the solvent and tend to precipitate from solution. Apreferred temperature range for this step of the process is about30°-100° C. and more especially about 45°-75° C.

After the BTDA solution has been adjusted to the appropriatetemperature, the aromatic triamine is added in small increments to theBTDA solution with stirring. The aromatic triamine will be added in aquantity corresponding to 0.33 molar portion per molar portion of BTDA.This reaction proceeds readily at the prevailing temperature andprovides an intermediate product consisting almost exclusively of achemical having the structure set forth in FIG. 1.

The aromatic triamine employed has the structure: ##STR6## In the aboveformula, R' represents an aryl group. Aryl in turn, for the purpose ofthis application, is defined as containing at least one 6-membered ringcontaining benzenoid unsaturation. Where aryl contains two or more6-membered rings, the rings can be joined by sharing a common pair ofcarbon atoms, e.g., as in a naphthyl grouping, or by being joined by avalence bond, e.g., as in a biphenyl grouping, or by a linking carbon,oxygen, or sulfur atom of the type defined as X in formula (1). The ringpreferably will contain only carbon atoms, but also may contain up tothree nitrogen atoms. Examples of suitable nitrogen-containing ringsinclude azine rings, diazine rings (1,2 or 1,3 or 1,4 rings), and thevarious isomeric triazine rings. Examples of suitable amines of thisclass include the isomeric tri(amino) substituted benzenes, toluenes,and xylenes, the tri(amino) substituted naphthalenes and biphenyls, andthe like. The preferred aromatic triamine is 2,4-bis (p-aminobenzyl)aniline (BPABA). Examples of triamines in which the aryl group containsone or more nitrogen atoms include 2,4,6-triaminopyridine,2,4,6-triamino- 1,3-pyrimidine, and 2,4,6-triamino-1,3,5-triazine(melamine).

The binyl substituted aromatic monoamine employed in the next step ofthe process has the structure:

    H.sub.2 N--R"                                              (3)

where R" is an aryl group such as a phenylene group, a naphthylenegroup, ##STR7## where X is as previously defined and one (1) valencebond of the aryl group bears a substituent having the structure:

    --CH═CH.sub.2

Examples of suitable compounds of this class include vinyl aniline,aminophenyl ethylene (APE) in alternate nomenclature, the alkylsubstituted vinyl substituted anilines such as the vinyl substitutedtoluidines and xylidines, the vinyl substituted naphthylamines, thevinyl substituted monoamino substituted biphenyls and the like.Aminophenyl ethylene (APE) is the preferred species. Certain of thevinyl substituted aromatic monoamines are known compounds reported inthe literature. Other of the compounds can be prepared by classicalsynthesis routes from commercially available materials.

The vinyl substituted aromatic monoamine, preferably3-aminophenylethylene (APE), is added in small increments with stirringto the solvent solution of the intermediate product prepared in theprevious step of the process. APE is a liquid at ambient temperature andcan be added in neat form or as a concentrated solution in the solventemployed in the earlier steps of the process. Good stirring and coolingshould be provided to maintain a reaction temperature within the limitspreviously described. The APE is added in a molar quantity equivalent tothe molar quantity of BTDA charged to the first step of the process. Thereaction product is a solution of a chemical consisting almostexclusively of the structure shown in FIG. 2.

The product of the preceding step can be converted to the desired vinylend-capped polyimide oligomer by effecting ring closure of the amic acidgroups by a dehydration reaction. Such methods are reported in the art,particularly the Barie patent U.S. Pat. No. 4,097,456 whose descriptionsare incorporated herein by reference.

Synthesis Method B

In the first step of this method substantially three (3) mols of certaindiesters of an aromatic tetracarboxylic acid such as a dialkyl ester of3,3'4,4'benzophenonetetracarboxylic acid dianhydride (BTDA) are reactedwith one (1) mol of 2,4-bis(p-aminobenzyl) aniline* in a suitablesolvent to form an amine salt. Letting the dialkyl ester of the aromaticcarboxylic acid be represented as: ##STR8## (the structure of R and R"'being defined infra), the principal product of this first reaction hasthe structure shown in FIG. 5.

In the second step of this method, a vinyl substituted aromaticmonoamine of formula (2) such as 3-aminophenylethylene (APE) is reactedwith the reaction product of the first step of the process to form acomplex amine salt whose principal component has the structure shown inFIG. 6.

In the third step of this method, the reaction product of the secondstep is heated to effect a ring closure to form imide groups. Theproduct of this step is the desired vinyl end-capped polyamide oligomer.

The dialkyl esters of the aromatic tetracarboxylic acid employed in thefirst step of the process have the formula: ##STR9## where R has thesame meaning as in formula (1) and where R"' is the moiety derived froma suitable alcohol, preferably an alkanol containing up to about 5carbon atoms. It will be recognized that 3-position isomers are possiblefor each diester, all of which are functional equivalents in the presentinvention. The desired dialkyl esters can be prepared by reacting 1molar portion of a dianhydride of formula (1), e.g., BTDA, with 2-molarportions of a lower alkanol containing up to 5 carbon atoms. An excessof the alkanol can be used as the reaction solvent and only the desireddialkyl ester will be formed.

In the first step of the process, the diester of the aromatictetracarboxylic acid, e.g., a diester of BTDA, is reacted with the BPABAin a suitable solvent. Typically, the solvent employed will be thealkanol from which the diester is prepared. If desired, however, otherlower alkanols containing up to about 5 carbon atoms and lower etherscontaining up to about 6 carbon atoms can be employed, preferably suchsolvents having atmospheric boiling points of less than 150° C. Ifdesired, mixtures of solvents can be employed, including mixtures of analcohol or an ether with water. Each of the chemicals is dissolved inthe minimum required quantity of the solvent.

This first reaction preferably is run by adding the BPABA solution insmall increments to the solution of the diester. Good stirring isprovided so that localized high concentrations of BPABA are avoided forreasons essentially similar to those noted respecting the first step ofSynthesis Method A previously discussed.

In the next step of the process, a vinyl substituted aromatic amine offormula (3), such as APE, is added in small increments with stirring tothe solvent solution of the intermediate product produced in theprevious step of the process. The majority of the vinyl substitutedaromatic monoamines are liquids at ambient temperature and can be addedto reaction in neat form, or as a concentrated solution in the samesolvent employed in the earlier steps of the process.

In the final step of this method, the reaction product of the secondstep is heated to effect a ring closure to form imide groups. This steppreferably is carried out employing the techniques disclosed in thepending Antonoplos et al application Ser. No. 956,708, filed Nov. 1,1978, which disclosure is incorporated herein by reference. TheAntonoplos et al application is owned by the assignee of the presentapplication.

Structure and Utility of Products

As previously noted, the vinyl end-capped polyimide oligomers of theinvention consist principally--virtually exclusively if proper synthesisprocedures are followed--of the compound having the structure shown inFIG. 3. In the initial synthesis step of Synthesis Method A, thedianhydride of formula (1) is difunctional and BPABA is trifunctional.As a consequence, some small percentage of low polymers of the compoundshown in FIG. 1 can be prepared, these polymers being principally dimersand trimers. As a consequence, when the ethylene substituted aromaticmonoamine of formula (2) is reacted with such polymers, low polymers ofthe compound shown in FIG. 2 also are prepared. Finally, when suchpolymers are converted to the ultimately-desired imides, low polymers ofthe compound shown in FIG. 3 or 3' also are prepared. The structure ofproducts of FIG. 3' is shown in FIG. 4 where R and R" have thepreviously-defined meaning and n and n' are small integers having valuessuch as 1, 2, and 3.

It has been observed that up to 50 mol % of the vinyl-substitutedaromatic monoamine employed in preparing the products of the inventioncan be replaced with a corresponding aromatic monoamine that is free ofan ethylene substituent. These modified products have structurescorresponding to those shown in FIGS. 2, 3, 4, and 6, except that up to50 mol % of the terminal ethylene groups --CH═CH₂ are replaced with ahydrogen atom. Only a small sacrifice in properties is suffered, whilethe cost of manufacture is reduced substantially.

The vinyl end-capped oligomers of the invention can be molded and heatcured to provide moldings having excellent strength, which strength isretained to a surprising degree even after the molded articles areheated for extended periods of time at elevated temperatures, e.g., 500or more hours at 315° C. (600° F.). Moreover, the products, before beingcured, have adequate flow to be processed satisfactorily. Free radicalgenerating polymerization initiators can be employed to acceleratecross-linking, but are not required.

In addition to being employed to prepare moldings, the vinyl end-cappedpolyimide oligomers can be used to lay down tough coatings on substratessuch as metals and to prepare laminates and/or composite structures. Toprepare such structures, a web of inorganic fibers such as glass,quartz, graphite fibers or the like, is impregnated with a solutioncontaining the polyimide solids. The impregnated web then is heated tomodest temperatures to cross-link the vinyl end-capped oligomer.

Where it is desired to prepare coatings, laminates or composites, it ispossible and usually desirable to prepare such compositions from one ofthe precursors of the polyimide oligomer. Either of the two previouslydescribed precursors, i.e., of the structure shown in FIG. 2 or FIG. 6,can be employed. When the precursors are heated, they form the polyimidestructure shown in FIG. 3 and upon further heating form cross-linkedproducts. The advantage of employing the precursors is that they have amuch higher solubility in solvents. As a consequence, higher solidslevels can be incorporated into the laminate or composite. It ispossible to prepare solutions which contain at least 30 weight % of theproduct of FIG. 2 in solvents such as NMP. It is possible to preparesolutions containing at least 50 weight % of the product of FIG. 6 insolvents such as the 1-5 carbon alkanols.

Where desired, the intermediates of FIG. 6 can be converted to a solidstate for storage or shipment by careful spray drying employing theconditions set forth in the Antonoplos et al application Ser. No.956,708, filed Nov. 1, 1978, and earlier incorporated herein byreference. These solids then can be dissolved in a suitable solvent ofthe type previously described to prepare coating and/or laminatingsolutions.

When used as coating compositions, the precursor solution should be laiddown on the substrate and heat cured at temperatures of 175° C. orhigher. To prepare laminates, the desired web should be impregnated witha precursor solution and heated to an elevated temperature for a timesufficient to convert the precursor solids to imides and liberate water.Drying the impregnated web for 60 minutes at 150° C. or 80 minutes at135° C. in a circulating air oven is usually sufficient. The dried websthen can be laid up and heated under pressure to cross-link the resinsolids. Modest pressures of the order of 15-200 psig are sufficient.Curing temperatures of the order of 177°-260° C. and preferably195°-220° C. are employed for curing times of the order of 1-12 hours.Optimum properties are developed by post curing the laminates forperiods of 16-48 hours at temperatures of about 260°-375° C.

The following examples are set forth to illustrate the principle andpractice of the invention to those skilled in the art. Where parts andpercentages are set forth, unless otherwise noted, they are parts andpercentages expressed on a weight basis.

EXAMPLE 1 Part A

Charge 60 ml of NMP and 48.3 grams (0.15 mol) of BTDA to a reactionvessel equipped with a high-powered stirrer. Heat the mixture to 150° C.with stirring to dissolve all of the BTDA and then cool to 60° C. Add asolution of 15.6 grams (0.05 mol) of BPABA dissolved in 20 ml of NMPdropwise over a period of 1 hour. Cool the vessel to maintain thereaction temperature at about 60° C. The product solids will consistprincipally of a compound having the structure shown in FIG. 1.

Part B

Add 17.9 grams (0.15 mol) of APE dropwise with stirring over a priod of1 hour to the solution of Part A while cooling the vessel to maintain areaction temperature of about 60° C. The product solids will consistprincipally of a compound having the structure shown in FIG. 2. The NMRspectrum of the product will show no detectable concentration of imidegroups.

Part C

Charge the product of Part B and 300 ml of toluene to a flask equippedwith a Dean-Stark Trap. Heat to reflux to effect a ring closure to formimide groups and remove the liberated water as an azeotrope. In about 4hours the theoretical quantity of water is collected. Recover theproduct by pouring it into about 2 liters of ethanol to precipitate aproduct consisting principally of a compound having the structure shownin FIG. 3'. The yield is essentially quantitative. Moldings preparedfrom this product have high-temperature strength properties essentiallysimilar to moldings prepared from the products exemplified in U.S. Pat.No. 3,845,018 and U.S. Pat. No. 3,897,349.

EXAMPLE 2 Part A

Charge 30 grams (0.66 mol) of ethanol and 49.3 grams (0.15 mol) of BTDAto a reaction vessel equipped with a high-powered stirrer. Heat themixture to reflux with stirring until all of the BTDA is esterified toform the diethyl ester of BTDA. The solution, when cooled to ambienttemperature, has a viscosity of about 2,500 cps at 25° C. Add a solutionof 15.6 grams (0.05 mol) of BPABA dissolved in 80 grams of ethanol,dropwise with stirring, over a period of about 15 minutes. The solutionthus prepared will contain about 35 weight % solids. Distillapproximately 80 grams of ethanol to prepare a solution containing about75 weight % solids. The product solids consist principally of an aminesalt having the structure shown in FIG. 5.

Part B

Add a total of 17.9 grams (0.15 mol) of APE dropwise with stirring overa period of 15 minutes to the product of Part A. The product containsabout 78 weight % solids and has a viscosity of about 75,000 cps at 25°C. The product solids consist principally of an amine salt having thestructure shown in FIG. 6.

Part C

Inject the product of Part B onto the rotating flask of a rotaryevaporator heated to about 90° C. and operated at about 1 mm of Hg. Thisproduct is partially imidized. Heat this product for 20 hours at 130° C.in a vacuum oven operated at 1 mm of Hg. to complete the imidizationreaction. The product is essentially identical to the product of Example1, Part C.

EXAMPLE 3

Impregnate six-inch squares of 181 E glass cloth (with an A-1100 finish)with the resin solution of Example 1, Part B. Dry these samples for 30minutes in a circulating air oven at 150° C. Extract a specimen of thedried fabric with NMP for chromatographic, NMR and I.R. analysis. Theextracted product will contain no evidence of carboxyl groups, thusindicating that all of the amic acid groups have been converted to imidegroups.

EXAMPLE 4

Lay up six pieces of 181 E glass fabric from Example 3 in the form of alaminate, place in a press under a pressure of 200 psig, and heat fortwo hours at 250° C. The laminate will be medium brown in color andcontain approximately 25 weight % resin. Postcure the laminate for fourhours at 650° F. (343° C.) and then an additional 15 hours at 700° F.(370° C.). No blisters or voids will be present in the postcuredlaminate.

EXAMPLE 5

Impregnate six-inch squares of 181 E glass cloth fabric (with an A-1100finish) with the resin solution of Example 2, Part B. Dry these samplesovernight at room temperature and then heat for 30 minutes in acirculating air oven at 190° C. The dried fabric will contain about 35weight % resin solids.

When an attempt is made to extract resin solids from the dried glassfabric with ethanol, only a small percentage of the solids areextracted. This fact suggests that the resin solids have undergone achemical reaction during the drying step. When the dried glass fabric isextracted with N-methyl-2-pyrrolidone (NMP), an extract is recoveredwhich is soluble to the extent of about 3 weight % in the NMP at roomtemperature. No detectable quantity of carboxylic acid protons will bepresent in the spectrum. The IR spectrum of the NMP extract isessentially identical to the product of Example 1, Part C.

EXAMPLE 6 Part A

Graphite tapes 5" wide are impregnated with the resin solution preparedin Example 2, Part B. The fibers are a commercial product sold under thename Celion 3000, have an O twist, and bear an NR 150-B2 surface size.The impregnated tapes are dried until the tapes contain 40 weight %resin solids. The prepregs are 2.5 mls thick. A laminate lay up is madefrom 32 plys with the prepregs all being aligned in one direction. Thelay up is laminated by a vacuum bag technique with the assembly beingheated from ambient temperature to 265° F. with the temperature beingincreased at a rate of about 5°/minute under a vacuum of 15 inches ofHg. The assembly is maintained for an additional 2-hour period under 15inches of Hg. The pressure then is reduced to the maximum vacuum thatcan be drawn and the temperature is increased to 485° F. at a rate ofabout 7° F./minute. The laminate is held at 485° F. for an additionalperiod of 2 hours. The laminate is cooled to room temperature over aperiod of 5 hours. The laminate is post cured by heating from roomtemperature to 650° F. at a rate of 5°-10° F./minute and then heatingfor 13 hours at 650° F. The temperature then is increased to 700° F. ata rate of 5°-10° F./minute. The temperature then is held at 700° F. foran additional 4 hours.

The Short Beam Shear, Flexural Strength, and Tangent Modulus ofElasticity, as determined by ASTM procedures at room temperature and at600° F., are substantially as set forth in Table I.

                  Table I                                                         ______________________________________                                                    Room Temperature                                                  Property    Value         600° F. Value                                ______________________________________                                        Short Beam Shear                                                                          12 ksi        7 ksi                                               Flexural Strength                                                                         200 ksi       140 ksi                                             Tangent Modulus of                                                                        20,000,000 ksi                                                                              19,000,000 ksi                                      Elasticity                                                                    ______________________________________                                    

Part B

Specimens of the laminates prepared in Part A, when heated for 300 hoursat 600° F., show a weight loss of only about 2%.

What is claimed:
 1. A product selected from the group consisting of:A.An end-capped polyimide oligomer whose principal component has thestructure: ##STR10## where R has the structure: ##STR11## where X is##STR12## or a bond; where R' is an aryl group; and where R" is an arylgroup bearing a substituent having the structure:

    --CH═CH.sub.2 ;

B. A first precursor of an end-capped polyimide oligomer of (A) whoseprincipal component has the structure: ##STR13## where R, R', and R" aredefined as above; C. A second precursor of an end-capped polyimideoligomer of (A) whose principal component has the structure: ##STR14##where R, R', and R" are as defined above, and where R"' is the alcoholmoiety from which the diester of the aromatic tetracarboxylic acid wasprepared.
 2. An end-capped polyimide oligomer whose principal componenthas the structure: ##STR15## where R has the structure: ##STR16## whereX is ##STR17## or a bond; where R' is an aryl group; and where R" is anaryl group bearing a substituent having the structure:

    --CH═CH.sub.2.


3. A precursor of an acetylene end-capped polyimide oligomer of claim 1,the principal component of said precursor having the structure:##STR18## where R has the structure: ##STR19## where X is ##STR20## or abond; where R' is an aryl group; and where R" is an aryl group bearing asubstituent having the structure:

    --CH═CH.sub.2.


4. A precursor of an end-capped polyimide oligomer of claim 1, theprincipal component of said precursor having the structure: ##STR21##where R has the structure: ##STR22## where X is ##STR23## or a bond;where R' is an aryl group; where R" is an aryl group bearing asubstituent having the structure:

    --CH═CH.sub.2

and where R"' is the alcohol moiety from which the diester of thearomatic tetracarboxylic acid was prepared.
 5. A product of claim 1, 2,3 or 4 in which R' has the structure: ##STR24##
 6. A product of claim 1,2, 3 or 4 in which R has the structure: ##STR25##
 7. A product of claim1, 2, 3 or 4 in which R has the structure: ##STR26## and where R' hasthe structure: ##STR27##
 8. A product of claim 1, 2, 3 or 4 in which Rhas the structure: ##STR28## R' has the structure: ##STR29## and R" hasthe structure: ##STR30##
 9. A coating and laminating varnish consistingessentially of a product of claim 3 dissolved in a solvent selected fromthe group consisting of N-methyl-2-pyrrolidone, cyclohexanone, diethylcarbonate, and gamma-butyrolactone.
 10. A coating and laminating varnishconsisting essentially of a product of claim 4 dissolved in a solventhaving an atmospheric boiling point of less than about 150° C. andselected from the group consisting of lower alkanols containing up toabout 5 carbon atoms, lower ethers containing up to about 6 carbonatoms, and mixtures thereof.
 11. A product of claim 1, 2, 3, 4, 9, or 10in which up to 50 mol % of the terminal --CH═CH₂ groups of R" isreplaced with a hydrogen atom.
 12. A process for preparing a product ofclaim 3 which consists essentially of:A. Dissolving at least 17 weight %of an aromatic tetracarboxylic acid dianhydride in a solvent at atemperature of at least 60° C., B. Maintaining a solution of step (A)containing substantially 1 molar portion of said aromatictetracarboxylic acid dianhydride at a temperature in a range of about30°-100° C. and adding substantially 0.33 molar portion of an aromatictriamine thereto, and C. Adding substantially 1.0 molar portion of avinyl substituted aromatic monoamine to the product of step (B);saidaromatic tetracarboxylic acid dianhydride having the formula: ##STR31##where R has the structure: ##STR32## where X is ##STR33## or a bond;said aromatic triamine having the formula: ##STR34## where R' is an arylgroup; and said vinyl substituted aromatic monoamine having the formula:

    H.sub.2 N--R"--CH.tbd.CH.sub.2

where R" is an aryl group; and the solvent employed in step (A) isselected from the group consisting of N-methyl-2-pyrrolidone,cyclohexanone, diethyl carbonate, and gamma-butyrolactone.
 13. A processfor preparing a product of claim 3 which consists essentially of:A.Adding, with stirring, a solution containing substantially 0.33 molarportion of an aromatic triamine to a solution containing substantially1.0 molar portion of a dialkyl ester of an aromatic tetracarboxylicacid, and B. Adding substantially 1.0 molar portion of a vinylsubstituted aromatic monoamine to the solution of (A);the dialkyl esterof the aromatic tetracarboxylic acid employed in step (A) having theformula: ##STR35## where R has the structure: ##STR36## where X is##STR37## or a bond; said aromatic triamine having the formula:##STR38## where R' is an aryl group; and said vinyl substituted aromaticmonoamine having the formula:

    H.sub.2 N--R"--CH═CH.sub.2

where R" is an aryl group; the solvent employed in Step (A) having anatmospheric boiling point of less than about 150° C. and is selectedfrom the group consisting of lower alkanols containing up to about 5carbon atoms, lower ethers containing up to about 6 carbon atoms, andmixtures thereof.
 14. A process of claim 12 or 13 in which R' has thestructure: ##STR39##
 15. A process of claim 12 or 13 in which R has thestructure: ##STR40##
 16. A process of claim 12 or 13 in which R has thestructure: ##STR41## and where R' has the structure: ##STR42##
 17. Aprocess of claim 12 or 13 in which R has the structure: ##STR43## andwhere R' has the structure: ##STR44## and R" has the structure:##STR45##